Researchers Add ‘New Piece to the Puzzle’ That is Celiac Disease

By Deborah Borfitz

September 10, 2024 | Celiac disease is a surprisingly common but substantially underdiagnosed autoimmune disorder estimated to affect 1 in 100 people globally. Left untreated, it can have “serious clinical consequences” for patients, including malnutrition, bone weakening, and potentially even a higher risk of certain cancers, according to Elena Verdu, M.D., Ph.D., professor of gastroenterology and director of the Farncombe Family Digestive Health Research Institute at McMaster University.  

It is particularly concerning in North America, where the estimated proportion of people unknowingly having the disease ranges between 60% and 95%. This stands in stark contrast to other parts of the world, such as Scandinavian countries, where the rates of diagnosis are much higher, says Verdu. 

The standard treatment for celiac disease is a lifelong gluten-free diet, which experts agree is not enough, she says. The pursuit of pharmacological interventions has in fact led to a slew of clinical trials in recent years, most targeting immune aspects of the disease that are thought to occur “mainly or only inside of the gut tissue.”  

But Verdu and her McMaster colleagues—Tohid Didar, Ph.D., associate professor in the school of biomedical engineering, and Sara Rahmani, a Ph.D. candidate in the Verdu and Didar labs—have recently discovered that the epithelium is an “active orchestrator of the immune response to gluten” and thus needs to be added as a target tissue for drug testing and development. Intestinal epithelial cells were shown to produce key molecules that make gluten “visible” to immune cells (T cell lymphocytes), which are now activated and mediate damage of the gut lining. The study was published recently in Gastroenterology (DOI: 10.1016/S0016-5085(24)00945-4). 

Verdu was trained as a medical doctor in her native Argentina and went on to do a research fellowship at the University of Lausanne in Switzerland, where her interest in research was piqued, she says. She pursued a Ph.D. so she could “discover new things and understand the origins of gastrointestinal diseases,” and thereafter joined the McMaster faculty. 

Didar has an undergraduate degree in mechanical engineering and, after going on to get his Ph.D. in biomedical engineering, started working with “cells and tissue and chips from an engineering perspective.” Before moving to McMaster, he held a postdoc position at the Wyss Institute for Biologically Inspired Engineering at Harvard University for four years where he worked on organs-on-chips systems. 

Rahmani, a chemical engineer by training, admittedly had to learn “everything from scratch” for the celiac disease research project that launched in 2016. “When I started, I had no knowledge of cell biology or immunology ... and organoids [utilized in the newly published study] were very new technology.”   

Diagnosable Condition

Unlike other gluten-related disorders, celiac disease is “very well defined” with a specific test to diagnose it, says Verdu. It primarily attacks the gut but can affect other systems, so it presents clinically with many symptoms and signs. It is brought on by a combination of genetics—variants HLA-DQ2 and, less often, HLA-DQ8—and ingestion of gluten-containing food, referring to certain proteins found in wheat, rye, and barley. 

This is decidedly different than a wheat allergy or (non-celiac) gluten sensitivity, she notes. A group of patients have been presenting in the clinic with varied, self-reported symptoms—e.g., abdominal cramps, tiredness, brain fog, among others—when they consume gluten-containing food. But there is no diagnostic test for gluten sensitivity, and doctors don’t know what is triggering the symptoms, although aversion to gluten (“nocebo effect”) could offer a partial explanation given all the demonization of gluten in the lay press. 

For celiac patients, completely removing gluten from the diet is in any case exceedingly difficult, says Verdu, and for many reasons. “Gluten is everywhere; we use it in processed foods [often as a thickening agent or for flavoring or coloring], and contaminations are frequent.” 

The gluten-free movement, as evidenced by modern-day offerings on restaurant menus and supermarket shelves, has a dark side for people diagnosed with celiac disease. As Verdu has heard directly from many patients, they are “torn when they go out for dinner or to social events and the waiter asks, ‘Yeah, but how sensitive are you?” 

‘Reductionist Approach’

The study finding that the inflammatory response in people with celiac disease can begin in the epithelium “adds a new piece to the puzzle,” says Verdu. It has long been known that the main driver of the disorder is an abnormal immune response to gluten. 

The protein sticks to certain molecules produced in the body by the HLA-DQ2 and HLA-DQ8 genes and that are present in antigen-presenting cells of the immune system. The molecules basically show gluten to the T cells that cause damage, she explains.  

“For many years, we thought that this only occurred inside of the gut tissue, and for that to happen gluten needs to get across the gut lining that separates what is in the lumen [flow-through cavity for digested food] and the rest of the body, including the immune system,” continues Verdu. It had also been long suggested that cells from the gut lining, under certain conditions, could take on an immune role, “but this had never been studied in the context of gluten and celiac disease.”  

To begin exploring the possibility that the gluten reaction could be initiated in the gut epithelium, researchers took tiny pieces of tissue from the region affected in patients with celiac disease to determine via immunofluorescence staining and flow cytometry if antigen-presenting molecules were present, she says. But that did not answer the question as to whether they were activating T cells there, which would be inherently complicated to get at using human tissue with its diverse immune cell population and different subtypes of gluten-presenting molecules. 

For this stage of the project, led by Rahmani, three-dimensional cell culture systems “organoids” were bioengineered to learn the functional consequences of the antigen-presenting molecules within a culture of pure epithelium. These organoids were created from the proximal parts of a humanized mice bred to express the celiac disease risk gene HLA-DQ2. The main characteristic of organoids is that they maintain molecular, genetic, and functional features of their native tissues, she explains. 

It’s a “reductionist approach” focused solely on intestinal epithelial cells and the disease of interest, Rahmani says, and found that when gluten is introduced to these epithelial cells, humanized celiac disease-related gluten-presenting molecules are expressed on intestinal epithelial cells under inflammatory conditions and activate T cells. When this inflammation is removed, expression of the molecules is reduced and “activation of T cells was minimal to none.” 

“We always thought that this could happen,” stresses Verdu, but it was never demonstrated because of the difficulty in isolating the critical components. The model system isolated only gut lining epithelial cells expressing the type of molecules found in celiac patients that present gluten to other antigens. Not all molecules that are part of the histocompatibility complex do that.  

Next Steps

The in vitro system developed for the study—an “organoid monolayer” engineered to express human molecules on a normal well plate—was intended to answer a specific biological question, says Didar. It enabled the team to “narrow down the specific cause and effect and prove exactly whether and how the [gluten] reaction takes place.”  

Didar came to McMasters University from the Wyss Institute in 2016. The original plan was development of a “celiac disease-on-a-chip” model. “We didn’t get to the chip part because it was really hard biology,” he says, adding that this could be a next step. “When the disciplines come together, better things happen.” 

Verdu says she is hopeful that companies developing therapies for celiac disease will not “overlook the epithelium” when eying their drug targets. She and Rahmani are currently discussing the possibility of investigating microbial regulation of the expression of antigen-presenting molecules in the gut lining and whether there are pathogens that increase this expression to create a predisposition to the disease.   

In their recent study, they found that modifying gluten with certain pathogens before putting it in the organoid monolayer system altered the degree of the resulting immune response, she notes. The quest is for cofactors allowing development of autoimmune processes since only some people with the culprit genes who consume gluten-containing foods develop celiac disease. 

As a doctor, one of Verdu’s central concerns is that diagnosed individuals are pretty much on their own currently when it comes to coping with the disorder. “This is an organic autoimmune disease where the only treatment is a diet; there is no therapy, so the burden of treatment is on the patient.”